Published OnlineFirst April 28, 2020; DOI: 10.1158/1078-0432.CCR-19-2958 CLINICAL CANCER RESEARCH | TRANSLATIONAL CANCER MECHANISMS AND THERAPY FS222, a CD137/PD-L1 Tetravalent Bispecific Antibody, Exhibits Low Toxicity and Antitumor Activity in Colorectal Cancer Models A C Matthew A. Lakins, Alexander Koers, Raffaella Giambalvo, Jose Munoz-Olaya, Robert Hughes, Emma Goodman, Sylwia Marshall, Francisca Wollerton, Sarah Batey, Daniel Gliddon, Mihriban Tuna, and Neil Brewis ABSTRACT ◥ Purpose: With the increased prevalence in checkpoint therapy Results: We demonstrated simultaneous binding of CD137 þ resistance, there remains a significant unmet need for additional andPD-L1andshowedpotentT-cell activation across CD8 therapies for patients with relapsing or refractory cancer. We have T-cell activation assays in a PD-L1–dependent manner with a developed FS222, a bispecific tetravalent antibody targeting CD137 CD137/PD-L1 bispecific antibody, FS222. FS222 also activated and PD-L1, to induce T-cell activation to eradicate tumors without T cells in a human primary mixed lymphocyte reaction assay, with the current toxicity and efficacy limitations seen in the clinic. greater potency than the monospecific mAb combination. FS222 Experimental Design: A bispecific antibody (FS222) was devel- showed no signs of liver toxicity up to 30 mg/kg in a non-human oped by engineering CD137 antigen–binding sites into the Fc region primate dose-range finding study. A surrogate molecule caused of a PD-L1 IgG1 mAb. T-cell activation by FS222 was investigated significant tumor growth inhibition and survival benefit, concom- þ using multiple in vitro assays. The antitumor efficacy, survival itant with CD8 T-cell activation, in CT26 and MC38 syngeneic benefit, pharmacodynamics, and liver pharmacology of a murine mouse tumor models. surrogate molecule were assessed in syngeneic mouse tumor mod- Conclusions: By targeting CD137 agonism to areas of PD-L1 els. Toxicology and the pharmacokinetic/pharmacodynamic profile expression, predominantly found in the tumor microenvironment, of FS222 were investigated in a non-human primate dose-range FS222 has the potential to leverage a focused, potent, and safe finding study. immune response augmenting the PD-(L)1 axis blockade. Introduction T cells, and dendritic cells (DC; ref. 4). Engagement of CD137 by its ligand CD137L results in receptor trimer formation, and subsequent Immunomodulatory mAbs are a promising approach for patients clustering leads to CD137 signaling cascade activation. This provides a with cancer. Immune checkpoint inhibitors targeting programmed cell survival signal to T cells, thereby sustaining effective T-cell activation death (PD)-1, PD-L1, and cytotoxic T-lymphocyte–associated protein and generation of immunologic memory. The primary functional role 4 are the most advanced immunotherapy agents for oncology. How- of CD137 in enhancing T-cell cytotoxicity was first described in ever, only a subset of patients benefit from long-term survival, and 1997 (5), and soon thereafter CD137 mAbs were proposed as anti- there remains an unmet clinical need (1). Although bispecific T-cell cancer therapeutics. engagers, such as blinatumomab (BLINCYTO) targeting CD3 and Clinical development of CD137 mAbs has been hampered by dose- CD19, are the most advanced next-generation immuno-oncology limiting high-grade liver inflammation associated with CD137 agonist modalities, their use is limited to hematologic malignancies and antibody treatment. Urelumab (Bristol-Myers Squibb, BMS-663513), further limited by acute safety concerns (2). We believe agonist a human IgG4 isotype antibody, was the first CD137 mAb to enter antibodies against specific costimulatory receptors from the tumor clinical trials, but these were halted after significant, on target, dose- necrosis factor receptor superfamily may represent the next stage in dependent liver toxicity was observed (6–8). This outcome was not solid cancer treatment. predicted because urelumab failed to preclinically identify liver inflam- CD137 (4-1BB) is a costimulatory molecule and widely known to þ mation due to its low affinity for the cynomolgus monkey target be upregulated on CD8 T cells following activation (3). CD137 þ molecule (9). More recently, clinical trials of urelumab in the treatment can also be expressed on activated CD4 helper T cells, B cells, of solid cancers were recommended; however, urelumab dosing in regulatory T cells (Treg), natural killer (NK) cells, natural killer these trials had to be limited and efficacy results were disappointing with no objective response reported in the 64 patients with solid F-star Therapeutics Ltd., Cambridge, United Kingdom. tumors treated with monotherapy (6). No dose-limiting toxicity has been observed with CD137 mAb Note: Supplementary data for this article are available at Clinical Cancer fi Research Online (http://clincancerres.aacrjournals.org/). utomilumab (PF-05082566, P zer), a human IgG2 isotype antibody, in dose-escalation phase I clinical trials dosing up to 10 mg/kg in phase I Corresponding Author: Matthew A. Lakins, F-star Therapeutics Ltd., Eddeva clinical trials of advanced cancer (6, 8). However, the overall objective B920, Babraham Research Campus, Cambridge CB22 3AT, United Kingdom. Phone: 01223948159; Fax: 01223410493; E-mail: [email protected] response rate with this antibody was only 3.8% in patients with solid tumors, potentially indicating that utomilumab has a weaker potency Clin Cancer Res 2020;26:4154–67 and clinical efficacy than urelumab, while having a more favorable doi: 10.1158/1078-0432.CCR-19-2958 safety profile (6, 8). Trials of utomilumab in combination with Ó2020 American Association for Cancer Research. radiotherapy or chemotherapy, as well as in combination with other AACRJournals.org | 4154 Downloaded from clincancerres.aacrjournals.org on September 25, 2021. © 2020 American Association for Cancer Research. Published OnlineFirst April 28, 2020; DOI: 10.1158/1078-0432.CCR-19-2958 Characterization of a CD137/PD-L1 Bispecific Antibody cancer without toxicity (7, 8), we believe there remains a need to Translational Relevance develop treatments that combine PD-L1 blockade and provoke We developed an mAb2 bispecific antibody for targeting CD137 strong CD137 agonism in safe and efficacious therapies that do not þ and PD-L1 in solid tumors which potently activated CD8 T cells rely on a combination approach. An alternative to combining CD137 in vitro only in the presence of PD-L1–expressing cells. Our and PD-L1 monotherapies is the development of a bispecific antibody þ surrogate molecule activated intratumoral CD8 T cells and that encompasses the two modalities. It is anticipated that such a effectively controlled tumor growth in syngeneic mouse tumor bispecific mAb could deliver superior antitumor efficacy over com- þ models without toxicity. We found that FS222 activates CD4 and bining monotherapies. There are existing preclinical approaches com- þ CD8 T cells in vitro with activity superior to the combination of bining CD137 mAb activity with PD-L1 mAb activity into bispecific monospecific, mAbs representative of those used in the clinic therapies. These can be subdivided into two broad range categories, currently, providing evidence that our tetravalent bispecific clinical non–IgG- and IgG-like molecules, both of which can be further candidate will provide greater benefit to patients than a combina- divided by their binding valency for each target. tion approach against both targets in solid tumors. Considering the Here, we describe a fully human, tetravalent, IgG bispecific antibody broad expression of PD-L1 in many solid tumors, FS222 may (mAb2, FS222) comprising a PD-L1–specific mAb with 5 amino acid provide therapeutic opportunities for patients with cancer who insertions and 7 amino acid substitutions in the CH3 region of the Fc remain challenging to treat. domain to create two binding sites forming an Fc fragment antigen- binding (Fcab) for CD137 (15). FS222 blocked PD-L1 and activated þ CD137 tumor-reactive T cells in a PD-L1–dependent manner. It demonstrated similar potency in primates, and preliminary toxicity antibody therapies, are ongoing with early results showing no dose- studies in this species showed significant pharmacodynamic (PD) limiting toxicities for doses up to 5 mg/kg and a 26% patient response responses and a lack of toxicity. A surrogate mouse cross-reactive rate for the combination of utomilumab and pembrolizumab (10). CD137/PD-L1 mAb2 with homologous mechanisms of action to PD-1 and its ligands PD-L1 (CD274, B7-H1) and PD-L2 (B7-DC) FS222 was observed to provide a substantial survival benefit in multiple deliver inhibitory signals that regulate the balance between T-cell mouse tumor models with no toxicity and showed potent in vivo PD activation, tolerance, and immunopathology. Consequently, PD-L1 changes related to antitumor immune responses. expression by cells can mediate protection against cytotoxic T lym- phocyte killing. Cancer, as a chronic and proinflammatory disease, subverts this immune-protective pathway through upregulation of Materials and Methods PD-L1 expression to evade the host immune response. PD-L1 expres- Production and characterization of a CD137/PD-L1 mAb2, sion has been shown in a wide variety of solid tumors (11), and clinical FS222 trials have shown the benefit of targeting PD-L1 in patients leading to The CD137/PD-L1 mAb2 molecule named FS222 consisting of the approval of three PD-L1–targeting mAbs to date: atezolizumab an IgG1 molecule comprising the